The present invention relates to a fail-safe control for an electronically controlled automatic transmission to be mounted on a vehicle, and more particularly to a fail-safe control of a transmission (T/M) by detecting the shift time.
In conventional electronically controlled automatic transmissions, in general, the gear ratio of the T/M and the state of the lock-up clutch (on-or-off) are determined in response to signals representing the degree of opening of a throttle and the car speed or the number of revolutions output from the T/M so that an actuator such as a solenoid or the like secured to the T/M is controlled.
In the conventional control method, a fail-safe control against an electric failure of a sensor or the actuator is generally performed.
However, in the conventional control method, the failures in the mechanical portion of a T/M, for example, valve sticking, and slippages of friction materials are difficult to subject to a sufficient fail-safe control, and a further improvement is required for the purpose of providings a more comfortable drive.